A distinction is made in the art of hose clamps between endless clamps made from tubular stock and open clamps which are adapted to be closed by a mechanical connection. Various types of open hose clamps are known in the prior art, a large number of which have a gap in the circumferential direction formed, for instance, by outwardly extending lobes or ears. These gaps in the circumferential direction of the clamping band represent a source of leakage danger because the hose is likely to be squeezed out into the gap under pressure of the medium carried by the hose. My prior U.S. Pat. No. 3,286,314 suggested in FIG. 5 to cover the gap by extending the inner band portion beyond the gap underneath a so-called "Oetiker" ear. This, however, produced another source of leakage in the form of the step formed at the end of the inner band portion, especially with thin hoses made of hard plastic material. The German Gebrauchsmuster 75 41 277.0 proposed an arrangement in which the inner band portion is fixed to the outer band portion ahead of the ear and a narrow tongue-like extension then covers the gap to engage in a pressed-out groove commencing directly at the opposite leg portion of the ear. The inadequacies stemming from the fact that only a narrow tongue-like extension covers the gap in this publication, were recognized and dealt with by the arrangements disclosed in my prior U.S. Pat. No. 4,237,584 in which the parts were so arranged that the full band width of the inner band portion came to lie underneath the so-called "Oetiker" ear. Further improvements in clamp structures devoid of any gap or step in the internal clamping surface, which proved highly successful, are disclosed in my U.S. Pat. Nos. 4,315,348 and 4,299,012. As the remaining gap under a so-called "Oetiker" ear after contraction thereof is relatively small, the full band width of the inner band portion covering the residual gap is normally adequate with a sufficiently strong clamping band material. However, the possibility of leakage increases with the circumferential length of the gap. The longer the gap, the greater the danger of leakage which results when the inner band portion is forced outwardly into the gap by the forces of the medium carried by the hose. The type of material and its thickness are a significant factor in the costs of the clamps. To reduce these costs, one therefore seeks to use thin clamping band materials as also less costly band materials. These considerations, however, are limited by other factors, such as holding ability and strength of the clamping band material to resist outward deflection into the gap on the part of the inner band portion.
So-called screw-type clamps, as disclosed in my U.S. Pat. No. 4,521,940 and in my aforementioned copending application Ser. No. 07/730,071, the subject matter of which is incorporated herein by reference, normally leave a relatively wide gap in the outer clamping band underneath the screw member of the threaded adjusting mechanism. Reinforcements in the inner band portion in the form of one or more ribs within the area lying underneath this gap, as proposed in my aforementioned copending application improved the holding ability of the inner band portion against outward deflection into the gap. However, even such reinforced inner band sections did not prove completely satisfactory under all operating conditions.